Interpretive Summary: Several strains of Salmonella have been identified as being resistant to multiple antibiotics. What is not known is if strains that are resistant to multiple antibiotics are also resistant to the killing effects of the antimicrobial interventions used in beef processing. The research project described herein was designed to determine if antimicrobial interventions currently in place in beef processing facilities are adequate for reducing the foodborne pathogen loads of beef carcasses contaminated with multiple drug resistant (MDR) Salmonella. The data presented here show that MDR Salmonella are reduced at least as effectively as E. coli O157:H7 and non-MDR Salmonella when treated with antimicrobial interventions currently in use at most U.S. beef processing plants. The E. coli O157:H7 strains used in this study included strains that are more likely to cause human disease and strains not typically found to cause human disease. No differences were detected in the abilities of these two groups to survive antimicrobial interventions. These results indicate that neither the drug resistance status of Salmonella nor the likelihood to cause human illness by E. coli O157:H7 influences the efficacy of the interventions utilized by the modern beef processing plants.

Technical Abstract:
Several strains of Salmonella have been identified as being resistant to multiple antibiotics. What is not known is if strains possessing multi-drug resistance (MDR) properties also have the ability to resist the killing effects of the antimicrobial interventions used in beef processing. The research project described herein was designed to determine if antimicrobial interventions currently in place in beef processing facilities are adequate for reducing the foodborne pathogen loads of beef carcasses contaminated with MDR-Salmonella. The data presented here show that MDR Salmonella are reduced at least as effectively as E. coli O157:H7 and non-MDR Salmonella when treated with antimicrobial interventions currently in use at most U.S. beef processing plants. The E. coli O157:H7 strains used in this study were divided into two groups, those that have a genetic polymorphism associated with human disease and strains not typically found to cause human disease. No differences were detected in the abilities of these two groups to survive antimicrobial interventions. These results indicate that neither the drug resistance status of Salmonella nor the likelihood to cause human illness by E. coli O157:H7 influences the efficacy of the interventions utilized by the modern beef processing plants.